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FIG. 5. Magnetic Induction.

So long as the magnet lies motionless in the coil it induces no currents. The field of force in the neighborhood of a magnet grows weaker as the distance from the magnet increases. When the magnet is plunged into the coil, the strength of the magnetic field in the vicinity of the coil grows stronger due to the approach of the magnet, and when it is withdrawn the field becomes weaker.

Currents are only induced in the coil when the magnet is moving, or in other words when the strength of the magnetic field is changing, either increasing or decreasing.

The currents generated in the coil are called induced currents. The action of the magnetic field in producing induced currents is termed Induction.

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If a piece of zinc is dipped in dilute sulphuric acid, the zinc will be attacked by the acid and replace hydrogen in it, the hydrogen appearing as bubbles on the zinc and passing off as a gas.

FIG. 6. Simple Voltaic Cell